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Re: Observations on 'strange observation on AO-40 S2 beacon'

Hello Gould,

I can confirm your observation. I am using an IC-910 under full CAT control
with SatPC32, and I always noticed some frequency drift. The author said
that it must be something outside the program because the calculation is
absolutely correct. Then I decided to buy a preampifier from DB6NT, and I
replaced my DB6NT downconverter, which was mounted directly to the G3RUH
patch (see www.dj1km.de). The downconverter comes in the same waterproof
cabinet. Then I took the downconverter down in the shack close to the
Transceiver where it stays in more or less constant temperature. Since then
the received signals are absolute stable. I can run AO40Rcv with the
IC-910 under CAT control, and the signal only moves a little bit after
switching on when the IC-910 VFO is warming up. BTW I have also installed
the quartz oven into the IC-910 because the original quartz is drifting too
much even after warm-up.


Tuesday, April 29, 2003, 1:01:44 AM, you wrote:

> I noticed some strange behavior.  As the satellite was approaching I
> expected the Doppler to increase in freq, and it did for a couple of
> measurements ( I was recording the time and frequency every 2 MA units).
> Then I noticed a decrease in the frequency and the waterfall (AO40Rcv)
> display indeed slanted to the left rather than the right.
> I scratched my head awhile, checked my relationship to the satellite again,
> wondered whether I had misread the dial.  Then the frequency increased
> again, then a slow increase, then a decrease.  Measured the time it took for
> a horizontal waterfall reading to scroll to the bottom of the screen (about
> 40 secs) to see what kind of resolution I could expect from the slope of the
> signal on the waterfall display.
> This went on for an hour confusing me more and more.  I started recording
> the time, freq and increase or decrease, more often, changed the audio
> cable, turned off everything else.  Nothing changed.
> Then I noticed that the Doppler shifted at the same time it got darker out.
> It was a very sunny day with spotty, large, thick cumulus clouds.  When one
> of these clouds moved in front of the sun and I saw the Doppler change I
> knew I was on to something.  As Stacey suggests it is a downconverter
> problem, there would be a rapid temperature change and it would be reflected
> in the downconverter.  Then when the cloud moved and the sun heated the
> converter I would see a pronounced shift in the waterfall slope.  Then it
> would level out as the temperature stabilized.  I watched this for about 20
> minutes longer, confirmed this a couple of more times and
> realized I would not get any valid data to graph.


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